Technische Projekte von Peter Rachow (DK7IH)

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20Mtr./14 MHz-SSB Transceiver: The receiver’s front end

Today it’s time to give a presentation about the receiver’s front end. When testing this one with an interfrequency of 9785 kHz I suddenly encountered that I had a strange demodulation phenomenon due to a very strong broadcasting station inside the if channel. After some days of listening and trying to decipher the words in English language I recognized that the „jammer“ was Radio Romania International transmitting on 9783 kHz. OK, folks, right beside the if-channel. Front end selectivity was the problem.

After conceiving about this problem, the conclusion that I drew was that with a receiver front end of only 2 tuned circuits the problem could not be solved to satisfy my demands on receiver purity. But a circuit of 3 LCs should do. So this solved the problem finally. So, here is the circuit of front end, rf preamp and first mixer: